1. Field of the Invention
This invention relates to centrifugal pumps of the type known as chopper pumps, which are structured to process fluids containing large-sized solids that must be cut or chopped by the pump. Specifically, this invention relates to an impeller and associated cutting elements which are configured to process entrained solids and exclude them from the area of the seal of the pump.
2. Description of Related Art
Centrifugal pumps of the chopper type are used in many and varied industries to process fluids that contain larger-sized solids, such as plastics or animal byproducts. Chopper pumps are typically characterized by having an impeller that is structured to contact a cutting element positioned adjacent the vanes of the impeller to exert a cutting or chopping action on the solid material entering the pump. The impeller and cutting structures positioned on the suction side of chopper pumps processes the majority of the solids content to a size that can be moved through the pump. However, some solids tend to also move toward the drive side of the impeller and may move inwardly toward the drive shaft of the pump.
When solids move toward the drive side, or back, of the impeller and inwardly toward the drive shaft, debris can become wrapped around the drive shaft and impede the operation of the pump. This is especially the case with fluids containing stringy solids. Debris behind the impeller can cause a build up in heat and wear on the impeller and can impede the cooling and lubrication of the seal elements. Solid material may infiltrate the seal and cause further problems with pump operation. Thus, some known chopper pumps have employed flushing mechanisms to clean behind the impeller.
Other known chopper pumps have used impellers designed with cutting elements located on or near the back side of the impeller and about the drive shaft to chop solid material in the location of the drive shaft. An example of an impeller and cutting element of the type described is disclosed in U.S. Pat. No. 5,460,482 to Dorsch. Some chopper pumps also use restrictor bushings around the shaft to keep larger solids away from the seal, as described in the '482 patent to Dorsch. Yet other chopper pumps use an open impeller design to reduce pressure behind the impeller so that solids are not drawn toward the back side of the impeller.
Prior art chopper pumps which employ a cutting element on the back side of the impeller require that the cutting element be positioned adjacent the impeller hub and/or in very close proximity to the drive shaft. As such, debris in the fluid, especially stringy material, can infiltrate all the way to the drive shaft and seal assembly before any chopping or cutting of the material takes place.
Thus, it would be advantageous in the art to provide an impeller and cutting element configuration in a centrifugal chopper pump that processes and excludes debris from behind the impeller before the debris can reach the drive shaft and seal assembly, thereby improving pump operation and the life of the pump.